1. Field of the Invention
The present invention relates to a workpiece taking-out apparatus which has a three-dimensional visual sensor mounted on a robot, recognizes a position and a posture of a workpiece existing in a container with an opening, and takes out the workpiece on the basis of the position and the posture.
2. Description of the Related Art
For example, there is widely known a method of acquiring, with respect to a plurality of workpieces contained in a basket-like container in an unpackaged state, data of a height distribution in a three-dimensional spatial area occupied by the workpieces (hereinafter referred to as “existing area of workpieces”) using a range finder or a three-dimensional visual sensor which projects pattern light. In addition, there has been proposed quite a few applications which use the height distribution data acquired by the method. As an example of such applications, there is a research for grasping the height distribution as an image (distance image) to perform object recognition on the basis of the image.
However, an example of such a research put in practice is hardly found. On the other hand, concerning taking-out of unpackaged workpieces, although examples of researches are found here and there, there are very few examples of researches put to practical use. Prior art relating to these techniques is indicated in, for example, Japanese Patent Application Laid-Open No. 9-277184 and Japanese Patent Application Laid-Open No. 10-315174.
Incidentally, there are several factors which make it difficult to put taking-out of unpackaged workpieces in practice. Among them, major factors are as described below.
Factor 1: A large number of unpackaged workpieces generally exist in a three-dimensionally irregular arrangement. If sensing is performed by a sensor, a few workpieces can be found out of them. However, it is actually difficult, with respect to the found plural workpieces, to decide an order of taking out the workpieces properly so as to take out the workpieces in order from one at the top, and smoothly take out the workpieces one after another.
Factor 2: Workpieces which could not be found by the sensor (hereinafter referred to as “unfound workpieces”) are obstacles in taking out the other workpieces. In other words, it is likely that, when taking-out means (robot) approaches a workpiece which it is about to take out next, the unfound workpieces interfere with a robot hand or the like.
It is considered that such factors can be overcome for the time being by finding and referring to height distribution in an existing range of the workpieces. However, a problem of resolution in height distribution measurement arises when measurement based upon the height distribution is actually applied to the workpieces. For example, when data of the height distribution is created in a practical time with respect to a relatively large existing area of workpieces as large as 1 m squares, it is inevitable that the resolution falls. Thus, in the case in which object recognition is performed using only that information to take out the workpieces, required accuracy cannot be obtained, and the taking-out of the workpieces is hindered.